President-elect Donald Trump speaks during a rally at the Lackawanna College Student Union in Scranton, Pennsylvania, Nov. 7, 2016.

China on Monday said it has lodged a diplomatic protest in Washington after United States president-elect Donald Trump took a phone call from the president of Taiwan, an island claimed but never ruled by its ruling Chinese Communist Party.

The "stern representations" came after Taiwan's democratically elected president Tsai Ing-wen called Trump on Friday to congratulate him on his election victory.

Foreign ministry spokesman Lu Kang said the protest had been lodged with the "relevant side," without giving details.

"The whole world knows about the Chinese government's position on the Taiwan issue," Lu told a regular news conference in Beijing.

"I think President-elect Trump and his team are also clear about it," Lu said, adding that Beijing has maintained contact with the incoming president and his team.

The Global Times newspaper, a sister paper of Communist Party flagship the People's Daily, said the phone conversation was the first at such a high level since Beijing and Washington established diplomatic ties and Washington withdrew diplomatic recognition from Taipei in 1979.

The fact that Trump even took Tsai's call showed "he still has much to learn about how to deal with the Sino-U.S. relationship, especially the Taiwan question," the paper said.

It said that while little could be gleaned from a single phone call, ties would be affected if Trump's administration were to cross "the bottom line set by the Chinese side."

"The world will be dragged into a mess if leaders all speak irresponsibly," the signed op-ed article said. "This shouldn't be allowed. Trump as future U.S. president should know what to say properly on different occasions."

Fundamental shift

Chan Chi Kit, assistant professor of communication at Hong Kong's Hang Seng Management College, said Trump may have been signaling a fundamental shift in U.S. foreign policy by taking Tsai's call.

"I think it's very clear that Trump intends to play the Taiwan card," Chan said. "Trump's battle lines were drawn up around not allowing U.S. industry to be relocated overseas ... with tax breaks for those that do not."

"Sooner or later, he is going to have to play the China card, so as to satisfy the electorate, and so this incident is him signaling to Taiwan, and to the rest of the world, that he isn't going to kowtow to China," he said.

He said that China is continuing to pile up diplomatic pressure on Taiwan since Tsai refused to publicly endorse the "One China" policy following her election earlier this year.

"I think the Taiwan government had already made mental preparation for various reactions from Beijing and from around the world," Chan added.

Tseng Chien-yuen, lecturer in administration at Taiwan's Chung Hua University, agreed that the phone call is likely a harbinger of closer commercial ties between the island and the U.S. under a Trump administration.

"He comes from a commercial background, where the principle that harmonious relations create wealth is a very important one," Tseng said.

"I think he's sending out a few political messages before he takes office to let people know that he will firmly support the U.S.-Taiwan relationship once he has taken office," he said.

'A new era'

Tsai, who heads the Democratic Progressive Party (DPP), pledged in her inaugural address to build a "united democracy that is not hijacked by ideology," in an apparent reference to her predecessor's closer ties with Beijing.

She also promised a "new era" in Taiwan politics, amid fears that ever-closer economic ties with China could undermine the island's democracy.

"Today, tomorrow, and on every day to come, we shall all vow to be a Taiwanese who safeguards democracy, freedom, and this country," Tsai said.

But while Tsai pledged to maintain peaceful ties with Beijing, mentioning landmark 1992 peace talks, she stopped short of endorsing Beijing's insistence that the island she governs is an inalienable part of a divided China.

The Kuomintang (KMT) nationalist party, which represented the island at the 1992 talks, had regarded itself as the legitimate rulers of a post-1911 Republic of China that had been "temporarily" relocated to Taiwan after losing a civil war to Mao Zedong's communists in 1949.

But Tsai was voted into power in a landslide victory from a platform that at the very least affirms the island's separate identity from mainland China.

Repeated polls have shown that many of Taiwan's 23 million residents identify as Taiwanese rather than Chinese, and that there is broad political support for de facto self-rule, if not formal independence.

Tweets on China

Meanwhile, Trump continued to lash out at China over the weekend, tweeting: "Did China ask us if it was OK to devalue their currency (making it hard for our companies to compete), heavily tax our products going into their country (the U.S. doesn't tax them) or to build a massive military complex in the middle of the South China Sea? I don't think so!"

The foreign ministry's Lu declined to comment on Trump's tweets on Monday.

"The China-U.S. economic and trade relationship has over many years always been a highly mutually beneficial one, otherwise it couldn't have developed the way it has today," he said.

"China and the United States maintaining good relations, a steadily developing relationship, accords with the joint interests of both peoples."

Trump, whose team hasn't taken State Department advice on contact with foreign leaders, takes office on Jan. 20.

'Provocative, damaging'

China's state news agency Xinhua on Monday issued a commentary warning against focusing on the president-elect's "sensational claims."

It said Trump should refrain from "light-headed calls for provocative and damaging moves on China."

Taiwan was governed separately from mainland China throughout the Japanese occupation (1895-1945) and since 1949, and has never been part of communist China.

Beijing has said it is willing to deal with any party in Taiwan, as long as they "recognize" that both sides of the Taiwan Strait belong to one China and don't allow the island to move towards independent statehood.Reported by Goh Fung for RFA's Cantonese Service, and by Hwang Chun-mei for the Mandarin Service. Translated and written in English by Luisetta Mudie.